Cities to visit (in order of my liking): Antwerp (Antwerpen), Bruges (Brugge), Ghent (Gent), Leuven and Brussels (Brussel). If you like to visit a modern vibrant city, start with Antwerp. It combines great history (architecture, paintings, museums, culture) with lots of pubs, restaurants and shops. If you like true medieval history, visit Bruges, also known as the Venice of the North. Ghent was the capital of Europe during the empire of Charles V. It is also a happening university town. However the center of student life occurs in Leuven. And yes, you should also visit Brussels. I typically compare a visit to Brussels to a visit to Washington D.C. If you can only pick one city in the US to visit, would it be Washington? Or San Francisco or New York?
What to drink? A visit to Belgium would not be complete without a visit to a couple of traditional pubs (cafes) and sample some of the 8700 different Belgian beers.
What to eat? Did you know French fries originated in Belgium? You won't be able to avoid them. In every town square, on many corners, you'll find a 'frituur' or small place to get a pointy bag with Belgian fries. Try it with mayonaise rather than ketchup, or try a couple of the various sauces on top of it.
Of course try a real Belgian waffle, the famous chocolates, speculoos, a bucket of mussels with fries, shrimp in tomato, eal in a green herb sauce, real Belgian endives or white asparagus.
Belgium is a cycling country. Many cycling champions came from Belgium. You'll find lots of people on a bicycle during the weekend making trip along the various trails. Checkout the fietsknooppunten blog for a sampling of trails and what to see along the trails. Or request the blog author for some recommended trails.
Leave a comment if you have specific questions about towns, seasons or customs.